EP0326248B1 - Dispositif d'affichage - Google Patents

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Publication number
EP0326248B1
EP0326248B1 EP89300264A EP89300264A EP0326248B1 EP 0326248 B1 EP0326248 B1 EP 0326248B1 EP 89300264 A EP89300264 A EP 89300264A EP 89300264 A EP89300264 A EP 89300264A EP 0326248 B1 EP0326248 B1 EP 0326248B1
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EP
European Patent Office
Prior art keywords
display
liquid crystal
crystal material
light
scattering
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EP89300264A
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German (de)
English (en)
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EP0326248A3 (en
EP0326248A2 (fr
Inventor
Andrew L. Dalisa
Richard Willey
James Mccoy
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Raychem Corp
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Raychem Corp
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Publication of EP0326248A3 publication Critical patent/EP0326248A3/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133553—Reflecting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/055—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect the active material being a ceramic
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/13743—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on electrohydrodynamic instabilities or domain formation in liquid crystals
    • G02F1/1375—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on electrohydrodynamic instabilities or domain formation in liquid crystals using dynamic scattering
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/13756—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering the liquid crystal selectively assuming a light-scattering state

Definitions

  • the invention relates generally to a display, and more particularly to a display utilizing a gain reflector and a display medium that may be switched between light scattering and non-scattering states.
  • Display devices may utilize liquid crystals.
  • the property of liquid crystals that makes them particularly useful in displays is the ability of certain liquid crystal materials to transmit light in a strictly aligned or non-scattering state, and to scatter light and/or to absorb it especially when combined with an appropriate dye, in a relatively free or scattering state.
  • An electric field may be selectively applied across the liquid crystals to switch between scattering and non-scattering states.
  • liquid crystal have excellent contrast between the characters displayed and the background, and high brightness in all ambient light conditions. It is also desirable that the display be free of front surface glare.
  • a known liquid crystal that can be used as a display medium is known as encapsulated operationally nematic liquid crystal material or nematic curvilinearly aligned phases (“NCAP”) liquid crystal material.
  • NCAP nematic curvilinearly aligned phases
  • the NCAP liquid crystal material scatters incident light.
  • incident light is transmitted through the NCAP material.
  • a pleochroic dye may be present with the liquid crystal material to provide substantial attenuation by absorption in the field-off state but to be substantially transparent in the field-on state. Any reference to the ability of liquid crystal to scatter and/or absorb light should not be limited to the scattering and minimal absorption properties of liquid crystals but should include the additional properties pleochroic dyes may impose on the optical properties of the liquid crystal.
  • the display medium of the display may also comprise other scattering-type display materials, e.g., dynamic scattering liquid crystal materials or ferroelectric ceramic materials comprising optically clear (Pb,La)(Zr,Ti)(O3) ("PLZT").
  • the dynamic scattering and PLZT display mediums are both switchable between light scattering and non-scattering states.
  • the use of a gain reflector can produce higher brightness in the field-on state when the illumination on the display is collimated or quasi-collimated. However, in the field-off state, brightness is also increased, thereby providing little or no improvement in the contrast ratio. When the illumination on such displays is diffuse, the gain reflector will not affect the brightness at all.
  • US 4693560 discloses a display comprising a display medium at a viewing side of the display and switchable between a first state in which incident light is at least one of scattered and absorbed and a second state in which the amount of such scattering or absorption is reduced, and a gain reflector means disposed behind said display medium.
  • a display comprising a display medium at a viewing side of the display and switchable between a first state in which incident light is scattered and/or absorbed and a second state in which the amount of such scattering or absorption is reduced, and a gain reflector means disposed behind said display medium for reflecting light passing through said display medium, characterised in that said gain reflector means comprises an offset gain reflector means for reflecting light angularly offset from the specular reflection from said display medium, said offset gain reflector means comprising an array of optical reflector elements disposed in a contiguous relation forming a sheet of optical elements, each optical element having in at least one orthogonal direction to the sheet a curved reflecting surface with a positive slope portion and a negative slope portion, wherein the length of one of said portions is greater than the other, said portion having the greater length having a curvature less than said other portion.
  • the invention provides a display having a relatively high contrast as well as brightness.
  • the invention provides a display that has excellent contrast and high brightness in all ambient light conditions.
  • the invention provides a display giving good performance in viewing conditions where glare is present.
  • the display disclosed herein is one which comprises a display medium disposed at a viewing side of the display.
  • the display medium is switchable between a first state in which incident light is at least one of scattered and absorbed, and a second state in which the amount of such scattering or absorption is reduced.
  • a gain reflector means for reflecting light transmitted by the display medium is located behind the display medium.
  • the display medium may comprise a liquid crystal material containing a dye that conforms to the structure of the liquid crystal material and a containment medium means.
  • the containment medium means induces a distorted alignment of the liquid crystal material which in response to such alignment scatters and absorbs light and which in response to a prescribed input induces the amount of such scattering and absorption.
  • the display also includes a color filter disposed between the liquid crystal means and the gain reflector means.
  • the display of the invention can produce relatively bright or white characters, information, etc. on a relatively dark background in collimated, quasi-collimated or diffuse lighting conditions.
  • the dark background may be produced by liquid crystal material that is randomly aligned in the field-off state wherein light incident on the liquid crystal material is scattered and absorbed.
  • the bright characters are caused, for example, by liquid crystal material that is in a field-on state or in ordered alignment and thus, substantially optically transparent. When the liquid crystal material is in the field-off state, only the relatively dark background appears. When a selected portion of the liquid crystal material is in order alignment, the field-on state, a very bright character will appear against the dark background to an observer within a viewing angle of the display.
  • Figure 1 shows a liquid crystal visual display indicated generally by reference numeral 10.
  • the display 10 includes two main components: a display medium 12 and a gain reflector 14.
  • Display medium 12 is at a viewing side 25 of display 10.
  • the gain reflector 14 is at a non-viewing side 27.
  • a color filter 20 may be located in between display medium 12 and gain reflector 14.
  • the display further includes a frame 16 comprising a plastic housing that provides environmental protection for the display medium and the gain reflector.
  • the display medium comprises a material that may be switched between a light scattering and a non-scattering state, e.g. a NCAP liquid crystal material, a dynamic scattering liquid crystal material or a ferroelectric ceramic such as PLZT, all of which are discussed in more detail hereinafter.
  • a material that may be switched between a light scattering and a non-scattering state e.g. a NCAP liquid crystal material, a dynamic scattering liquid crystal material or a ferroelectric ceramic such as PLZT, all of which are discussed in more detail hereinafter.
  • both the field-on and field-off states are increased in brightness. Although the brightness is increased, the contrast ratio of the display remains the same. The perceived appearance of such a display may be slightly better than without the gain reflector. In some cases, the appearance may be worse.
  • the effective gain of a gain reflector depends upon the degree of collimation of the incident light. In the scattering state, light incident upon the reflector will be relatively diffuse. The gain of the reflector for diffuse illumination will be close to unity. In the non-scattering state, light incident on the reflector may be much more collimated (depending upon the design of the illumination system) and therefore the effective gain will be greater than unity.
  • contrast ratio brightness (on) X gain/brightness (off) X gain
  • displays utilizing the NCAP liquid crystal material have been found to have effective gains of 2.2 in the non-scattering state and 1.1 in the scattering state.
  • the display medium 12 may comprise a liquid crystal cell 21 that includes a liquid crystal material 22.
  • the optical characteristics of the liquid crystal material are a function of whether or not a prescribed input is applied to the liquid crystal material.
  • the prescribed input is preferably of the electromagnetic type and, more particularly, an electric field.
  • a schematic representation of a circuit 24 for selectively applying or not an electric field to the liquid crystal material 22 is illiustrated in Figure 1.
  • a circuit 24 may include an electric power supply 26, such as a battery, and a switch 28.
  • the electric power supply may alternatively be a source of alternating current.
  • the circuit 24 is connected by electrical leads 30, 31 to electrodes 32, 33 positioned on opposite sides or surfaces of liquid crystal material 22 of cell 21.
  • the electrodes 32, 33 are substantially optically-transparent, and may be formed on optically-transparent substrates 52, 53, respectively.
  • the liquid crystal material 22 preferably is of the type (NCAP) disclosed in US-A-4435047. As is represented schematically in Figure 3, such liquid crystal material 22 preferably is formed of operationally nematic liquid crystal 40 in a plurality of volumes 42 formed in or defined by a containment medium 44.
  • the liquid crystal 40 preferably is optically transparent, and the containment medium preferably also is optically transparent.
  • the liquid crystal material 22 has mixed therewith a dye 46, for example a pleochroic or diochroic dye.
  • a liquid crystal material without a dye may be utilized to form the display medium.
  • Each volume 42 may be discrete or alternatively the liquid crystal 40 may be contained in a containment medium, such as a polymer encapsulant that tends to form a multitude or capsule-like environments containing the liquid crystal material.
  • the liquid crystal 40 may be more or less confined to an approximately spherical or otherwise curvilinear surface of a containment cavity. Such cavities, however, may be interconnected, for example, by one or more channels or passages.
  • the liquid crystal would preferably be in both the discrete volumes or cavities and in the interconnecting passages.
  • the internal volumes of respective capsules may be fluidly coupled via one or more interconnecting passages.
  • the pleochroic dye 46 in the liquid crystal 40 will absorb some of the light transmitted therethrough, and the degree of such absorption is a function of whether or not an electric field is applied to the liquid crystal material and of the magnitude of such field.
  • the degree of such absorption in the field-on condition of the liquid crystal should be zero or as close to zero as possible to maximize transmission of incident light.
  • the dye alignment follows the alignment of the liquid crystal 40, as is illustrated schematically in Figures 3 and 4, for example, and is explained in further detail in the above-mentioned patent. Therefore, when the liquid crystal structure is in distorted alignment, the dye will provide a relatively substantial amount of light absorption. However, when the liquid crystal 40 is in parallel alignment, e . g ., like that liquid crystal shown in Fig. 4, light absorption by the dye will be minimized. As the magnitude of electric field is increased or decreased, the amount of distortion of the liquid crystal material will vary, and the amount of absorption by the dye also will correspondingly vary.
  • the liquid crystal structure In field-on operation, i . e . the non-scattering state, as shown in Figure 4, the liquid crystal structure is considered to assume a generally parallel alignment. Since the ordinary index of refraction of the liquid crystal 40 in field-on condition is matched to that of the containment medium 44, the liquid crystal material 22 becomes essentially optically transparent and light incident thereon is not refracted at interfaces between the liquid crystal and containment medium. During such field-on operation, incident light is transmitted through liquid crystal cell 21.
  • Field-off operation, i . e the scattering state, of the display is depicted in Figure 3.
  • Light which is incident on liquid crystal material 22 is refracted, scattered and absorbed.
  • Such scattering is effected because the extraordinary index of refraction of the liquid crystal 40 is different from the index of refraction of the containment medium 44.
  • the light is absorbed by the dye 46.
  • the index of refraction of the liquid crystal varies depending on whether an electric field is applied across the liquid crystal material.
  • the index of refraction of containment medium 44 and the ordinary index of refraction (the index when an electric field E is applied) of the liquid crystal 40 should be matched as much as possible when in the field-on state to avoid scattering, thereby tending to maximize light transmission.
  • the liquid crystal is in the field-off state, there will be a difference in the indices of refraction at the boundary of the liquid crystal 40 and the containment medium.
  • the containment medium tends to distort the natural liquid crystal structure to present to a great extent at the interfaces of the liquid crystal and surfaces, the extraordinary index of refraction (the index with no electric field E) characteristic of the liquid crystal; and such extraordinary index of refraction is different from the index of refraction of the containment medium. Therefore, when in such distorted alignment condition, there is a difference in the indices of refraction at the interface between the liquid crystal and containment medium, which causes refraction and, thus, scattering of light incident thereon.
  • Electrode 33 may, for example, form a common electrode surface while the opposed electrode 32 comprises patterned electrodes having multiple electrode portions that can be selectively energized to apply the electric field to selected portions of the liquid crystal material. For instance, as is well known in the art, electrode 32 may be divided into seven electrically isolated segments, each of which may be selectively energized to display various numerical characters. Electrode 32 may also be configured to form a dot matrix display comprising a plurality of dots or pixels arranged in column and rows. A row is enabled to accept display information in parallel via the column lines.
  • the liquid crystal material 22 including dye 46 may be prepared in the form of an emulsion of liquid crystal and containment medium which is subsequently dried or cured.
  • the liquid crystal material may take the form of a plurality of individually formed capsules of liquid crystal in the containment medium.
  • the containment medium is formed of a polyvinyl alcohol (PVA).
  • PVA polyvinyl alcohol
  • the liquid crystal is dispersed or entrapped in a latex containment medium.
  • substrates 52, 53 of liquid crystal cell 12 may comprise a polyester film, such as Mylar®, that has been precoated with a layer of indium tin oxide (ITO) to form the electrodes.
  • ITO indium tin oxide
  • the film has been precoated with a 80 to 500 ohms per square layer of ITO. Materials other than ITO may be used to form the electrodes of the apparatus of the present invention.
  • Latex entrapped NCAP liquid crystal comprises the entrapment of liquid crystal in a latex medium.
  • the latex is a suspension of particles.
  • the particles may be natural rubber or synthetic polymers or copolymers.
  • a latex medium is formed by drying a suspension of such particles.
  • the display medium 12 may comprise a liquid crystal cell that consists of a dynamic scattering liquid crystal material.
  • a dynamic scattering liquid crystal material is switchable between light scattering and non-scattering states.
  • an electric field passed through a dynamic scattering liquid crystal material disrupts the alignment of the liquid crystal material such that light is scattered or refracted.
  • the dynamic scattering liquid crystal material is optically clear.
  • the scattering effect in the dynamic scattering liquid crystal material is obtained when no electric field is applied.
  • Dynamic scattering liquid crystal materials are well known in the art, and as such, they will not be described in any detail herein. Dynamic scattering is described in the following articles: J.L. Fergason, et al., "Liquid Crystals and their Applications", Electro-Technology , January, 1970, p.41; and E.H. Heilmeier, et al.,"Dynamic scattering: A new electro-optic effect in certain classes of nematic liquid crystals", Proc . IEEE , Vol. 56, p.1162, 1968.
  • display medium 12 may comprise a scattering/non-scattering ferroelectric ceramic system.
  • Ferroelectric display systems are also well known in the art, and as such, they will not be described in detail. They may comprise optically clear (Pb,La)(Zr,Ti)O3 ceramic materials (PLZT).
  • the PLZT ceramic like the encapsulated operationally nematic liquid crystal material and the dynamic scattering liquid crystal material, is switchable between light scattering and non-scattering states.
  • the PLZT ferroelectric ceramic is described in the following articles : A.L. Dalisa, et al., "Convolution Scattering Model for Ferroelectric Ceramics and other Display Media", Proc . IEEE , Vol. 61, n. 7, pp. 981-991, July 1973. G.H. Heartling, et al., "Recent improvements in the optical and electro-optic properties of PLZT ceramics", Ferroelectrics , Vol. 3, p. 269, 1972
  • the color filter 20, described above, is utilized to provide a color display.
  • Filter 20 may be constructed from any transparent, non-scattering color material.
  • the color filter may be formed from colored glass or a dyed plastic material.
  • the color filter, color sheet or lens 20 may be virtually any color, for example red, green, yellow, orange, etc.
  • Color filter 20 may be laminated to the front or backside of display medium 12. Preferably, however, the filter is laminated to the back of the display medium.
  • color filter 20 may be spaced from the back of display medium 12 such that an air gap exists therebetween, as is represented by spacing "d1". If the electrodes of the display medium are configured to form pixels, the spacing "d1" should be approximately less than 10% of the minor dimension of the pixels.
  • the display medium 12 is switchable between a non-scattering (clear) state and a scattering (opaque) state.
  • the colored material behind the display medium or portion thereof in the field-on state is visible to an observer or an observing instrument 58 on viewing side 25 of the display.
  • the color filter 20 may be eliminated, and instead gain reflector 14 may be selectively screen printed with colored dyes, for example fluorescent dyes, as shown generally by reference numeral 54.
  • the colored dyes provide a colored pattern that can produce color for pixels in the display.
  • the fluorescent dye increases brightness due to its ability to absorb light over a wide range of frequencies and then to emit this light at a particular color.
  • incident light represented by light beams 60, which is refracted when it passes through display medium 12, is reflected back from a known gain reflector 14 as light beams 62 that make up a gain lobe 64.
  • the incident light is also reflected as glare, as will be explained in more detail below, from the surface of display medium 12.
  • the reflected light 62 is not uniformly distributed but is concentrated to some degree.
  • the limiting case of a gain reflector would be that of a plane mirror. In that case, all the light in a collimated incident light beam remains collimated in the reflected beam, which is propagating in a direction such that the angle of incidence equals the angle of reflection.
  • the light distribution in the reflected beam may be broad or narrow.
  • the gain of such a reflector may be defined as the ratio of the light flux into a detector (with a fixed solid angle at a given angle to the surface) from the gain reflector to that from a Lambertian reflector.
  • the distribution of reflected light from the gain reflector broadens and therefore the gain decreases.
  • the limiting case occurs when the incident light beam, or illumination from viewing side 25, for example, is diffuse or Lambertian. This results in a Lambertian reflected light distribution, that is a gain of unity.
  • the gain reflector may comprise, as shown in Figure 2, an opaque, plastic or metal substrate 50 having a reflective coating 55.
  • the coating can comprise a thin layer of silver or aluminum, for example a sputtered aluminum coating, that has a rough or uneven surface.
  • the type of gain reflector that may be utilized in the display of the present invention is based on that described in US-A-4241980.
  • This gain reflector is commercially available from Protolite Corporation, Palo Alto, California. It is sold under the trademark Mirror Image. This gain reflector and a method of its manufacture are also described in a paper entitled: G. Mihalakis, "Large Screen Projection Displays", Proc . SPIE , Vol 760, p. 29, 1987.
  • This gain reflector comprises an array of optical elements that are juxtaposed to form a matrix of rows and columns. These optical elements have both convex and concave image-forming portions such that the optical axes of the elements are at an angle to the normal to a substrate of the gain reflector.
  • the individual optical elements typically have dimensions smaller than an observer can resolve at the determined viewing distance, and the convex and concave portions are shaped to provide overlapping images at that viewing distance.
  • the glare or specular reflection represented by light beam 66, is caused by light reflected by the planar reflective surface that is parallel to the principle plane of the gain reflector, i . e ., the display surfaces comprising, e . g ., the front and rear surfaces of display medium 12 including any transparent overlay or cover therefor.
  • the gain reflector i . e ., the display surfaces comprising, e . g ., the front and rear surfaces of display medium 12 including any transparent overlay or cover therefor.
  • the gain lobe 64 (reflected gain), comprising reflected light beams 62, is distributed around the direction of the specular reflection (glare), light beam 66, that is the angle of incidence ⁇ 1 equals the angle of reflection ⁇ 2.
  • the available gain decreases.
  • the present invention utilizes an offset gain reflector, i . e ., one that separates the direction of the specular reflection or glare from the direction of the reflected gain or light.
  • the light distribution field or pattern from a display having an offset gain reflector 14' is schematically illustrated in Figure 5 where the reflected gain is represented by a light lobe 64', comprising light beams 62', and the specular reflection (the reflected glare) is represented by light beam 66' .
  • the specular reflection or glare from the surfaces of display medium 12 is not in the same direction as the maximum brightness and contrast of the display, i . e ., the specular reflection is angularly offset from light reflected (light beams 62′) by the offset gain reflector.
  • the optical elements of the offset gain reflector shown in Figures 6 and 7 comprise asymmetrical wave forms that angularly offset the reflected light.
  • this modified gain reflector produces the light distribution pattern illustrated in Figure 5.
  • the mathematical surface of the gain reflector described in US-A-4241980 is based on the joining (splining) together of individual low order curved optical elements in a manner which results in a shape with a continuous first derivative (tangent) and a defined second derivative (curvature).
  • This two dimensional (splined) wave form is then modulated in a non-standard fashion by another wave form defined on the orthogonal axis.
  • the result is a three dimensional surface of smoothly joined optical elements having, as discussed, both convex and concave image-forming portions.
  • the optical power (the ability to spread light) of this array of elements is exactly the same as the optical power of a single element.
  • the single optical element in the gain reflector may in principle be any smooth continuous function with two zero crossings; see, e . g ., Figure 6 where the "x"-"y" plane is the inflection or zero plane and all "x" direction waveforms undergo zero crossing. But, in practice, it has been restricted to second order functions, e . g ., a circle, an ellipse, a parabola, or a hyperbola.
  • the angle into which a ray of light will be reflected by an optical element will depend on the slope of the curve at the point of interest, i . e , the steeper the slope, the larger the angle.
  • the boundaries of the light reflection pattern are determined by the steepest negative and positive slopes.
  • a second important consequence of slope dependence is that the light distribution pattern is element size independent.
  • the smaller element will intercept and act upon a smaller portion of the incoming light, but will distribute that light at the same angle or pattern as would a larger element. This is true whenever both the large and small elements have the same shape.
  • the surface consisting of a single row of three dimensional optical elements may be constructed by introducing some repeating wave form on the axis orthogonal to the primary wave form. This is done by making the element size proportional to the amplitude of the modulating wave.
  • the surface of the gain reflector of US-A-4241980 is configured by joining to each element its mirror image sized in such a manner that the combined length of this compound element is held constant, independent of the size of the primary element. This pattern may be repeated indefinitely creating a continuous sheet or array of optical elements in rows and columns as described in US-A-4241980.
  • the gain reflectors produced commercially by Protolite have been symmetric, and thus they produce symmetric light distribution fields or patterns.
  • the offset gain reflector 14' schematically illustrated in Figures 5-7 incorporates an asymmetric wave form element, which, as illustrated, may be a section of a rotated ellipse.
  • Other asymmetrical forms such as a rotated parabola, a rotated hyperbola or any high order curve, may be utilized to construct an offset gain reflector.
  • the offset gain reflector 14' is made up of an array of asymmetrical optical elements "A" each, e . g ., comprising a section of a rotated ellipse. As illustrated in Figure 7, the result is a curve having a much greater portion of its length with a positive slope "B” then a negative slope "C". Since the positive and negative slope regions send reflected light to opposite sides, positive slope side "B", having more area, will receive more light. Furthermore, the positive slope side has less curvature and thus does not distribute light over as wide an angle as does the negative side "C". Since the distribution angle is smaller, the light remains more concentrated and thus brighter. The net result is an array or sheet of optical elements which, when light is directed normal to the elements, reflects that light in a distribution pattern which is brighter on one side than the other.
  • Figure 8 illustrates the reflected light pattern from the above-described offset gain reflector wherein the angle of reflection from 0° is plotted on the "x" axis and brightness on the "y” axis.
  • the offset gain reflector reflects incident light in a pattern that is brighter at "E", i . e ., it is brighter on one side of the "y" axis than the other.
  • the offset gain reflector may be fabricated in the manner described in the above-discussed SPIE paper by Mihalakis, i . e ., by utilizing a Computer Numerical Control micro-milling system to form the asymmetrical optical elements.
  • Such an offset gain reflector can be manufactured by Protolite.
  • display 10 in quasi-collimated light depends to a great degree on controlling the angle of the light incident on different portions of display medium 12. Since in most applications, incident light is not completely collimated nor perpendicular to the display surface, different portions of display medium 12 and the gain reflector, for example the top and bottom surfaces, if the display is orientated vertically, will receive light at different angles. This will, in general, produce different optical performance and, therefore, noticeable differences in appearance.
  • the display of the invention is operable in all ambient lighting conditions to produce a display having excellent contrast and brightness.
  • the display is effective at night (very low, less than 100 foot lamberts ("Fl"), or zero ambient light), in bright sun (ambient light greater than 1000 Fl), and on cloudy days or indoors (ambient light 100 to 1000 Fl).
  • incident light represented by light beam 60 (see Figures 2,5)
  • light beam 60 is transmitted through the display medium in the non-scattering state, where it is reflected, shown as light beams 62, by means of the gain reflector to create a display observable by an observer 58.
  • dye in the NCAP liquid crystal cell produces light absorption.
  • the brightness of the display in the field-on state is increased because the light experiences little absorption or scattering as it passes through the liquid crystal cell. It is then reflected into a narrow distribution by the gain reflector and then passes through the liquid crystal cell again.
  • the liquid crystal cell In the field-off state, the liquid crystal cell will scatter and absorb the diffuse incident light and provide little or no gain. Therefore, even in diffuse lighting conditions, the combination of the gain reflector and the liquid crystal cell provide high brightness and contrast.
  • the display apparatus displays the selected numeral, character or other information to an observer 58 on viewing side 25 within the viewing angle of the display.
  • the area between the energized electrodes may appear very light (or colored) against a very dark background.
  • the liquid crystal material that is not located between the energized electrodes is in the field-off state. Thus, that material still scatters and absorbs incident light, creating a very dark appearance, from both the viewing and non-viewing sides.
  • the display is adaptable to such displays as vehicle dashboards and control panels.
  • the display produces unique display improvements including: (1) the overall brightness of the display when the display medium is in the non-scattering state is increased while the display brightness in the scattering state is not changed, yielding an increase in the contrast ratio when the display is illuminated by either collimated or quasi-collimated light; (2) an improvement in the brightness and contrast ratio of the display even when illuminated by diffuse light; and (3) the capability of angularly separating the reflected light distribution (reflected gain from the gain reflector) from the specular reflection (glare from the display medium in front of the gain reflector).

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mathematical Physics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Dispersion Chemistry (AREA)
  • Liquid Crystal (AREA)
  • Devices For Indicating Variable Information By Combining Individual Elements (AREA)
  • Optical Elements Other Than Lenses (AREA)

Claims (14)

  1. Dispositif d'affichage comprenant un support d'affichage (12) situé du côté d'observation du dispositif d'affichage et pouvant commuter entre un premier état dans lequel de la lumière incidente est diffusée et/ou absorbée et un second état dans lequel l'intensité de cette diffusion ou absorption est réduite, et un moyen réflecteur à gain (14) disposé à l'arrière dudit support d'affichage (12) pour réfléchir la lumière passant au travers dudit support d'affichage (12), caractérisé en ce que ledit moyen réflecteur à gain (14) comprend un moyen réflecteur à gain excentré (14') pour réfléchir une lumière angulairement excentrée du fait de la réflexion spéculaire produite sur ledit support d'affichage (12), ledit moyen réflecteur à gain excentré (14') comprenant une matrice d'éléments réflecteurs optiques (A) disposés côte à côte en formant une feuille d'éléments optiques (A), chaque élément optique (A) ayant, dans au moins une direction orthogonale à la feuille, une surface réfléchissante incurvée avec une partie à pente positive (B) et une partie à pente négative (C), la longueur de l'une desdites parties étant supérieure à celle de l'autre, ladite partie de plus grande longueur ayant une courbure inférieure à celle de l'autre partie.
  2. Dispositif d'affichage selon la revendication 1, caractérisé en ce que ledit support d'affichage (12) comprend un matériau du type cristal liquide (22) contenu dans un moyen de rétention (44) pour induire un alignement distordu dudit matériau du type cristal liquide (22) qui, en réponse à cet alignement, a au moins l'une des fonctions de diffusion et d'absorption de la lumière et qui, en réponse à une entrée prédéterminée, réduit l'intensité de cette dispersion et de cette absorption.
  3. Dispositif d'affichage selon la revendication 2, caractérisé en ce que ledit matériau du type cristal liquide (22) est biréfringent et possède un indice de réfraction ordinaire, en présence de ladite entrée prédéterminée, qui est sensiblement adapté à l'indice de réfraction dudit moyen de rétention (44) pour minimiser la réfraction et la diffusion de la lumière, et un indice de réfraction extraordinaire, en l'absence de ladite entrée prédéterminée, qui est différent de l'indice de réfraction dudit moyen de rétention (44) pour provoquer une réfraction et une diffusion de la lumière.
  4. Dispositif d'affichage selon la revendication 3, caractérisé par un moyen d'entrée pour appliquer ladite entrée prédéterminée audit matériau du type cristal liquide (22), ledit moyen d'entrée comprenant un moyen à électrodes (32, 22) sur les surfaces opposées dudit matériau du type cristal liquide pour appliquer un champ électrique aux bornes dudit matériau du type cristal liquide.
  5. Dispositif d'affichage selon la revendication 1, caractérisé en ce que ledit support d'affichage (12) comprend un matériau du type cristal liquide à diffusion dynamique (22).
  6. Dispositif d'affichage selon l'une quelconque des revendications 1 à 4, caractérisé en ce que ledit support d'affichage (12) comprend un matériau du type cristal liquide nématique encapsulé (22).
  7. Dispositif d'affichage selon la revendication 6, caractérisé en ce que ledit matériau du type cristal liquide nématique encapsulé contient un colorant (46).
  8. Dispositif d'affichage selon la revendication 7, caractérisé en ce que ledit colorant est un colorant pléochroïque dont la structure a pour effet d'absorber la lumière lorsque ledit matériau du type cristal liquide présente un alignement distordu.
  9. Dispositif d'affichage selon la revendication 1, caractérisé en ce que ledit support d'affichage (12) est un matériau sélectionné dans le groupe constitué d'un matériau du type cristal liquide nématique torsadé et d'un matériau du type cristal liquide supertorsadé.
  10. Dispositif d'affichage selon la revendication 1, caractérisé en ce que ledit support d'affichage (12) comprend un matériau céramique ferroélectrique de type PLZT.
  11. Dispositif d'affichage selon l'une quelconque des revendications précédentes, caractérisé en ce qu'il comprend en outre une source d'éclairage par l'avant.
  12. Dispositif d'affichage selon l'une quelconque des revendications précédentes, caractérisé par un filtre coloré disposé entre ledit support d'affichage (12) et ledit moyen réflecteur à gain (14).
  13. Dispositif d'affichage selon l'une quelconque des revendications 1 à 11, caractérisé en ce que ledit moyen réflecteur à gain (14) comporte un motif de matériaux fluorescents colorés.
  14. Dispositif d'affichage selon l'une quelconque des revendications précédentes, caractérisé en ce que chaque élément optique (A) comprend deux surfaces réfléchissantes, l'une concave et l'autre convexe, et en ce que chaque élément optique (A) est uniformément joint au suivant, sans aucune discontinuité.
EP89300264A 1988-01-25 1989-01-12 Dispositif d'affichage Expired - Lifetime EP0326248B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US147756 1988-01-25
US07/147,756 US4991940A (en) 1988-01-25 1988-01-25 Gain reflector-liquid crystal display

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EP0326248A2 EP0326248A2 (fr) 1989-08-02
EP0326248A3 EP0326248A3 (en) 1990-08-16
EP0326248B1 true EP0326248B1 (fr) 1994-07-13

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EP (1) EP0326248B1 (fr)
JP (1) JP2857159B2 (fr)
CA (1) CA1302545C (fr)
DE (1) DE68916658T2 (fr)

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Also Published As

Publication number Publication date
JPH023011A (ja) 1990-01-08
DE68916658D1 (de) 1994-08-18
DE68916658T2 (de) 1994-11-10
EP0326248A3 (en) 1990-08-16
EP0326248A2 (fr) 1989-08-02
JP2857159B2 (ja) 1999-02-10
CA1302545C (fr) 1992-06-02
US4991940A (en) 1991-02-12

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